1. Field of the Invention
The present invention relates to electric switches and, more particularly, to a press button type safety switch, which automatically trips off upon an overcurrent and, which enables the user to view the on/off status of the safety switch from its outer appearance.
2. Description of the Related Art
A variety of electric switches, including seesaw switches and press button switches are known. In early days, a press button switch has only ONxe2x86x92OFF function, and cannot trip off automatically upon an overcurrent. In order to eliminate this problem, a variety of safety switches are developed. Regular safety switches are commonly of seesaw switching type.
FIGS. 1A and 1B show a seesaw switch 1 invented by the present inventor. This design of seesaw switch 1 uses a plank 11 to move a conducting plate 12 between on/off positions. When an overcurrent occurred, the conducting plate 12 automatically trips off the contact 121.
FIGS. 2Axcx9c2E show an overload protective press button switch according to the prior art. This structure of overload protective press button switch comprises a housing 31, the housing 31 having a top opening 311 and two open chambers 313 and 314 separated by a partition plate 312, a metal contact unit 33 installed in the housing 31, a switching mechanism 35, a press button assembly 32, and a linkage 34. The linkage 34 comprises a spring member 342 supported on the partition plate 312, a press member 341 mounted on the spring member 342, and a swivel holder 344 pivoted to the housing 31. The swivel holder 344 has a guide hole 343, which receives the press member 341, and a positioning portion 345 connected to the switching mechanism 35.
When pressed the press button assembly 32, the press member 341 is forced downwards to compress the spring member 342 and to bias the swivel holder 344, thereby causing the switching mechanism 35 to switch on the metal contact unit 33. When switched on, the spring member 342 pushes the press member 341 back to the initial position. The upper part I of this overload protective press button switch is similar to the design of the aforesaid prior art press button switch. The lower part II of this overload protective press button switch is similar to the design of the aforesaid prior art seesaw switch. This design is similar to Yu""s Taiwan utility model no. 83365 (equivalent to U.S. Pat. No. 5,262,748) with the exception of the additional press button assembly 32. The swivel holder 344 is equivalent to Yu""s seesaw plank. This structure of overload protective press button switch is complicated, resulting in high manufacturing cost and inconvenience of use. When the push button assembly 32 pressed to the position shown in FIG. 2C, and the swivel holder 344 is biased leftwards, the metal contact unit 33 is switched on. When the user released the hand from the push button assembly 32, the push button assembly 32 is moved to the position shown in FIG. 2D. Viewing from the outside, it shows no difference between the position of FIG. 2B and the opposition of FIG. 2D, therefore the user cannot know on or off status of the switch when viewed from the outside. For on/off indication, a complicated indicator circuit must be installed.
The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a press button type overload protective safety switch, which enables the user to know xe2x80x9con or off status of the switch from the outer appearance of the switch. It is another object of the present invention to provide a press button type overload protective safety switch, which automatically trips off upon an overcurrent. It is still another object of the present invention to provide a press button type safety switch, which is simple and inexpensive to manufacture. To achieve these and other objects of the present invention, the press button type safety switch comprises a housing, the housing having a holding chamber separated by a horizontal partition wall thereof into an upper open chamber and a lower receiving chamber, and a through hole through the horizontal partition wall in communication between the upper open chamber and the lower receiving chamber; a plurality of terminals installed in the lower receiving chamber of the housing and electrically connected to external power supply; a switching mechanism installed in the lower receiving chamber of the housing and controlled to switch on/off the circuit of the terminals; a linkage adapted to switch on/off the switching mechanism, the linkage comprising spring members supported in the upper open chamber of the housing, a press button assembly supported on the spring members in the upper open chamber of the housing, and an actuating mechanism mounted in the through hole of the housing and connected between the press button assembly and the switching mechanism and controlled by the press button assembly to switch on/off the switching mechanism, the actuating mechanism comprising a conical spring mounted on the partition wall, a press member supported on the conical spring and partially inserted into the through hole of the housing, and a seesaw plank pivoted to the housing, the seesaw plank having a guide groove, which receives the press member for enabling the seesaw plank to be biased by the press member to switch on/off the switching mechanism, and a positioning portion disposed at one end thereof and connected to the switching mechanism; wherein: the linkage comprises at least one locating rod; the seesaw plank comprises at least one top hook adapted to hook on the at least one locating rod of the press button assembly to hold the press button assembly in a position where the spring members in the upper open chamber of the housing maintained compressed by the press button assembly when the press button assembly pressed by the user to switch on the switching mechanism.